DE2204473C3 - Device for determining temporal mean values of the current and / or the concentration of gas components in a measurement gas - Google Patents

Description

V ₁ U) =

V ₁ l /) d /

V ₁ , ■ k ,,, ID V ₁ U) ■ k ,,

V, U)

4 (1

a second multiplier (13) for the multiplication -r, connected downstream of the averaging unit (12). of the mean value VVftJ with the concentration value k, f and a subtracter (14) connected downstream of the multipliers for determining the difference

"ill

4. Apparatus according to claim 3, characterized by an averaging device (12) connected downstream Subtractor (16) for forming the difference

V, .- V ~ _h (t)

and a divider (17) for forming the quotient

V ₁ U) IV ₁ , V ₁ (/ | Α (/ (

Wl

5. Device according to one of claims I to 4, wherein the measurement gas by the breathing gas Test persons is formed, characterized in that b-> room air serves as an additional gas.

V ₁ U) = -

k, U)

k, U)

j A, li)

j. / fu.d,

where k, (0 is the concentration of the gas component of interest in the measurement gas and V (t) is the flow of the measurement gas as a function of time /. The mean values of interest V ₁ (O and K ₁ (I) of the respective gas component are obtained exactly if Using a fast concentration meter (time constant small compared to the fluctuation time of the flow), e.g. mass spectrometer, the concentration k, (0 and using a flow meter, e.g. pneumotachograph, the measuring gas flow V (t) is continuously measured and the respectively measured Values are evaluated electronically in accordance with the equations given. However, fast concentration meters are technically very complex and therefore also very expensive.

The device according to US Pat. No. 3,595,063 ensures cheaper use; With this device, an average concentration value Fi (I) is already obtained at the outlet of the mixing vessel.

rer concentration meter, is required. The partial flow results - if a flow meter is also used - to

V (O-IO) - V (i),

where V (t) would represent the (calculated) mean value of the measuring gas flow recorded with the additional flow meter. The advantage of cost savings would, however, be bought with the disadvantage of increased measurement inaccuracy, at least within the range of V ₁ φ.

The reason for this inaccuracy is that also when use of an additional flow meter k with the method known from US-PS device always either the value (0 or the further required for the calculation of V ₁ (O value V OX never However, both values can be recorded exactly at the same time. For example, with unsteady flow through the mixing vessel, the current V (Odes measuring gas can be measured exactly and thus also precisely averaged over a predeterminable time period Γ; however, this time period T only represents an estimated mean value for the mixing time of the vessel represents (actual mixing time is dependent on the time behavior of the current V (OX so that in case of deviations of the actual mixing time from the estimated value corresponding to different concentration values k (t) are obtained. in contrast, if the measurement gas flow V (t) held by the mixing vessel at a constant value , e.g. through constant suction of the gas (in pulmonary function diagnostics If a breathing mask is put on the test person and the breathing gas is constantly pumped out of the breathing mask), defined mixing times ^ T and thus also exact concentration values k, (0 The value V (t) (in lung function diagnostics, the so-called breathing time volume) is not, however more measurable, and thus the value V ₁ (tyno be determined.

The object of the invention is to provide a measuring device that can be used without significant technical as well as additional costs, the desired measured values can be recorded exactly.

The object is achieved according to the invention with a device of the type mentioned at the outset in that the added gas (V _f (t)) contains the gas component to be measured in a known constant concentration (k, i) that the additional gas source and the line with are connected to the measuring gas at the inlet of the mixing vessel, so that the additional gas (V / (0) is added to the measuring gas flow (V (t)) w so that a constant total m

(V ,. = V + V ₁ )

from Meßgusstrom and / usat / gasstrom and that a flow meter in the flow path of the Measurement gas odt: the additional gas is switched on before mixing.

In the device according to the invention, the mean partial flow V, (I) of the examined gas component in the measurement gas results

V ₁ U) V _,; -IiHiU) V ₁ U) - k, i.

where Vi (I) is the flow of the gas supplied from the gas source, k, i is the concentration of the gas components examined in this gas. Vc is the constant total current

V (O + V ₁ (t)

in the mixing vessel and k, c (0 means the concentration of the gas component in the total flow Vo.

In the above equation, the values Va and k, i are each known. The value TcZ (t) can be read off directly on the concentration meter. This value corresponds exactly to the mean concentration value of the examined gas component in the total flow Vg, because the total flow Vc through the mixing vessel is constant. The Wen Ve (O can be obtained directly by switching the flow meter into the flow path of the additionally supplied gas, or indirectly by measuring the value V (t) by means of a flow meter in the flow path of the measuring gas and then

Vr (t) = Vc- V (t)

is calculated. The averaging of V nes V, (t) over the period Γ (corresponds to mixing time T = " des

Vu

Mixing vessel with the volume V ₀ ) is preferably performed electronically.

To determine the mean partial flow sought

mung V ₁ (O are therefore measured variables required, the

are either known in advance (Vc: k, i) or

by means of the device according to the invention, exactly ίο can be determined (k, c (t): Vt (O)) . The value V ₁ (t) sought is thus also - as desired - exactly

determinable.
The mean value that may still be searched for

the concentration of the investigated gas component η in the measurement gas results from knowing the exact one

Partial flow mean value V, (t) to

V, (M

f (M

M. the device according to the invention can thus simultaneously mean values of both the current and also the concentration of gas components

4 ") determine measuring gas exactly.

The technical and additional expense required compared to the known devices is low, since in the device according to the invention only one additional gas source (in the investigation

-, 0 chung of breathing gas is used as a gas source z. B. simply used the ambient air) with a corresponding Connection line to the mixing vessel and with regard to the devices that have hitherto been operated in a purely non-stationary manner only a constant current generator, z. B. an im

v> Total current path switched on (relatively cheap) pump with constant pump configuration. are needed.

Another advantage of the device according to the invention results from the fact that / u- determination of the value V ₁ (I) is no longer - as before - directly the

mi Meßgasstromwert "(ι) must be known. but that the value V (I) can be calculated by reference to the value of V (I).

Especially in pulmonary function diagnostics so that the possibility is given to the breathing gas flows

(Keep the vial path free of flow meters, whereby, on the one hand, the test subject is less stressed and on the other hand due to the defined flow conditions, the significant! . reduced dead space as well

the independence of the measurement of viscosity and Density fluctuations of the breathing gas also improve the overall measurement result

Since the composition, temperature and direction of flow of the additionally supplied gas (pump power is set so that Vc> Vmat (0) is constant at all times), simple, in certain areas even non-linear flow meters, e.g. cheap flow meters, can be used to determine VVY ^ Furthermore, such a system does not require any valves.

The invention is illustrated by means of two figures, which show an exemplary embodiment (lung function diagnostics) represent for a measuring device, explained in more detail below:

In FIG. 1, a test person I breathes through a gas line 2 into a mixing vessel 3 of volume V _n . In the line 2 there is a trap 4 for separating solid and liquid components in the respiratory gas of the test person 1.

A further gas line 5 is also connected to the line 2. The connection of the gas line can of course also take place before trap 4. The gas line 5 opens with its free end in the Ambient air. In this line 5, a flow meter 6, z. B. standard aperture or meat see nozzle, as well as a fan 7, which uei setting desired pressure values in the breathing gas supply line 2 is used.

The mixing barrel 3 has an output line 8 for the gas flowing into the vessel 3. At the output line 8 is a concentration meter 10 for the examined gas component in the respiratory gas of test person 1, e.g. oxygen concentration meter and / or carbon dioxide concentration meter, switched on. In the output line 8 there is fener a pump 9 of adjustable constant pumping power.

In the operating state of the device according to FIG. 1, due to the constant pumping power of the pump 9 in the mixing vessel 3 a constant gas flow

Vo = V (I) ₊ V _E (t)

generated, where V (t) aev respiratory gas flow of test person 1 and Vf (t) mean the air flow sucked in by the pump 9 via the line 5. The pump power is selected so that the relationship Vt,> V _m "(t) (ie Vi (I)> 0) is fulfilled at any point in time. This ensures that the breathing gas exhaled by the test person 1 reaches the mixing vessel 3 completely and cannot, for example, partially escape via the line 5 into the ambient air.

With such a mode of operation, there is thus - as desired - the one already mentioned at the beginning Relationship:

VjU) = Y ₁ , ■ Α;,;! /) L ^: '/ in ■ k, i.

The quantity S / ₍ , results directly from the pumping power of the pump 9. The current Vi (t) is tapped as an electrical signal at the flow meter 6. The concentration value k, i of the air flow Vi (ι) is known from the composition of the room air ( approx. 21% O), 0% COj), and the concentration value k7, (:} can be read directly from the spraying concentration meter 10.

The calculation of the value V, (ι) is preferably carried out by means of the computing device shown in FIG.

A multiplier 11 is provided to form the product V _r , ■ k ,,, (t). A mean value generator 12 is used to calculate the mean value Vj- (t) V «

(Averaging time T -

Vl,

). In a further multiplier 13, the product of V, (i) and k, i is formed

κι and by means of a subtracter 14 the difference between the output signals of the multiplier 11 and multiplier 13. The value V, (t) resulting at the output of the subtracter 14 is displayed by means of a suitable display device 15.

The computing device according to FIG. 2 also has a second subtracter 16 to form the difference

Vr, - VV (i)

κι and a dividing member 17 for calculating the Quotient

A ₁ IM =

f'ilf)

The concentration value fT, (t) is displayed by means of a concentration display device 18.

1 sheet of drawings

Claims (3)

Patent claims: 1. Device for determining temporal Miuel values of the current (Vi (%)) and / or the concentration (kj (tj) of gas components in a measuring gas flow (V (OX in particular of oxygen and / or carbon dioxide in the respiratory gas of a test person, consisting of a mixing vessel , to which an additional gas source is assigned to supply an additional gas to the measuring gas, a pump with constant power in the mixed gas flow for drawing a constant gas flow from the mixing vessel and a concentration meter for the gas component to be measured in the output line, characterized in that the mixed gas (VE (t)) the gas component to be measured in a known constant concentration β, ε) contains that the additional gas source (5) and the line (2) with the measurement gas are connected to the inlet of the mixing vessel (3) so that the additional gas (V _e (t)) is added to the measuring gas flow (V (O) in such a way that there is a constant total flow in the outlet line (8) of the mixing vessel (Vc = V ₊ Ve) results from measuring gas flow and additional pass flow and that a flow meter (6) in the flow path the measuring gas or the additional gas is switched on before they are mixed 2. Apparatus according to claim I _1, characterized in that 'τι flow path (5) of the additional gas, a fan (7) is switched on. 3. Apparatus according to claim 1 or 2, characterized by an electronic computing device with a first ^ multiplier (11) for the measured values Vc and Tu; (0 · an averaging unit (12) for the measured value The invention relates to a device for determining temporal mean values of the current (V ₁ (O) and / or the concentration (k, (0)) of gas components in a measuring gas flow (V (OX in particular of ■ 5 oxygen and / or carbon dioxide in the breathing gas of one Test persons, consisting of a mixing vessel, which is used to supply an additional gas to the measuring gas additional gas source is assigned to a pump with constant power in the mixed gas flow in removal of a constant gas flow from the mixing vessel and a concentration meter for the to measuring gas component in the outlet line. From US-PS 35 95 063 a device of this type is already known in which by means of two pumps transversely ι ί to the actual flow path of the measuring gas (respiratory flow) an additional gas is sucked into a mixing container with constant power and an equal quantity of Mixed gas is sucked out of the mixing container again. The additional gas is a 2n gas that does not include the gas component actually to be measured Gas mixture examined in a gas analyzer and the Concentration of the gas measured. In pulmonary function diagnostics, however, it is not just the concentration value that is of interest; Of particular interest is also the averaged over a certain period of time current dei gas to be measured component, which in turn result from the mean concentration value abhängL Here, the averaged over a period of time T stream V (0 and k is the concentration (0 of a gas component in a measurement gas completely generally